A harp is a musical instrument with strings that are varied in a graduated manner both in length and in thickness. Typically a harp has a body, a neck (also called an "arch") having an end connected to the upper end of the body, and a post at the other end of the neck extending to the lower end of the body. The body comprises an elongate case and an elongate soundboard (also called a "table"). The harp strings are stretched between the neck and the soundboard and are secured to a strip that is fixed centrally and axially on one or both sides of the soundboard. The pull of the strings is resisted on the bass end by the post (also called a "pillar") and on the treble end by the neck. The neck or arch is also called the harmonic curve and is the result of an effort to employ lengths that are correlated to the thicknesses of the strings so as to yield a pleasant tone when the strings are plucked. The sinusoidal quality of the harmonic curve also contributes to the graceful quality of the harp's appearance.
Harps vary in size from the large concert or classical harp to the small folk harps such as the Celtic harp, Minstrel harp, and Paraguayan harp, but all of which have essentially the components referred to above. The smaller harps are not simply miniature versions of the larger harps, but suffer certain defects in tonality and response due in substantial measure to the relative shortness of the soundboard and case; larger harps have a greater tolerance for various structures used to secure the components of the harp. The present invention is directed to a number of improvements to the harp structure which have particular applicability to small harps such as the folk harp, but which nevertheless can also be put to good use on the larger, concert or classic harps as well as on other instruments that use a soundboard that is subject to the forces of tensioned strings. In this regard, the concepts of this application have broad application to all such instruments such as lyres, guitars and similarly fretted instruments, violins, violas, cellos, bases and even pianos and harpsichords.
One embodiment of the invention is directed to an improvement in the relationship of the soundboard to the case. Traditionally, the soundboard or table is made from Sitka Spruce and is glued and screwed to a sound case (also called a soundbox) which is in the form of a trapezoidally-shaped trough or a trough which is a semicircle in cross-section. In either example, the radius of the semi-circle or diagonal of the trapezoid is much greater at the bass end of the soundboard than at the treble end. The underside of the case is formed with openings which allow access to the strings, so that knots can be tied to secure the strings, and also help to vary the resonance characteristics of the sound case so that its response to the frequencies of the strings covers a broad spectrum of sound.
To assist in the resonance response, the sound case is usually made of thin materials, such as several thicknesses of veneer stock glued and cross-laminated to give it strength in two dimensions. To resist the deforming action of the pull of the strings on the soundboard, bracing is typically placed inside at regular intervals. This bracing can be of wood, but is often made from metal castings. The pull of the strings imparts an upward curve to the soundboard which, because the soundboard is rigidly connected to the case, translates into a force that brings the edges of the sound case closer together. The bracing is needed to resist this pull, but the addition of metal bracing has a deleterious effect on the tone of the harp, imparting definite irrational overtones affecting the quality of the harp's tone or voice. The bracing also adds to the weight of the harp.
Besides the effect of bracing, the gluing and screwing of the soundboard to the sound case also has a restrictive influence on the modes in which the soundboard can vibrate. The vibration of the strings forces a vibration of the soundboard through the principle of forced resonance. Any natural resonances which the board has which coincide with the fundamental or overtone frequencies of the strings will thus be strengthened by the board. When the board is attached in the traditional manner, it acts like a clamped membrane, resulting in a built-in hysteresis generating a poor response to longer sound wavelengths and an increase in higher overtones. Thus, the voice of small harps tends to be high and to lack the mellow quality found in large concert harps, in which the soundboard is long enough to compensate for the clamping effect. In addition to the foregoing drawbacks, if the soundboard of a harp becomes damaged, its removal is a major undertaking requiring the services of a trained harp repairman.
In accordance with the first embodiment, an improvement is made to soundboards by movably securing the soundboard to the case. More specifically, the soundboard is secured such that at least a first side edge of the soundboard is movable relative to the adjacent side edge of the case when the soundboard is pulled by the strings. In a practical aspect of this embodiment, retaining rails are placed on both sides of the sound case to hold the soundboard in place. A simple molding is secured to the outer edge of the sound case, for example a wooden molding is glued thereto, and the soundboard is prevented from being pulled away from the sound case by the presence of these rails. At the treble end of the sound case, a wooden cap is glued in place which resists the upward thrust of the soundboard at that end. Importantly, because the soundboard is free to move against the surface of the retaining rails, no deforming forces are exerted against the sides of the sound case and the need for internal bracing is thereby eliminated. Also, because the soundboard is not rigidly attached to the sound case, the entire surface of the board is less restricted in its vibrational mode and it is able to respond to a wider spectrum of musical sound. The result is a sound which is both louder and mellower. Because the board is not glued and screwed to the sound case, if there is any injury to the board it is a simple matter to disassemble the harp and replace the soundboard. The damaged board can be pulled out and a new one pushed in.
In a second embodiment, a mechanism is provided for substantially enhancing the resonance of the soundboard. Part of the tonal quality of a harp depends on the principle of sympathetic resonance, in which the entire set of properly tuned strings forms a sympathetic resonance system. When any one string is plucked, it produces its fundamental tone as well as a series of overtones or harmonics. These harmonics will correspond to the fundamentals and overtones of other strings in the system. For example, the first overtone of a low "G" will correspond to the "G" an octave higher and its second overtone will correspond to the "D" above that "G". At the same time, the third overtone of the low "G" will correspond to the first overtone of the "G" an octave above it. Thus, when the low "G" is plucked, its overtones are reinforced by other strings through the sympathetic resonance system. The soundboard is the medium through which this is accomplished.
In normal harp construction, many of the sound waves remain concentrated in the soundboard, but many others travel through other parts of the harp where their ability to excite sympathetic resonance is lost and where they are not able to properly excite the air molecules. This partly results from the hysteresis referred to above, due to the rigid clamping of the soundboard. The shape of the board itself also tends to distribute the sound in a dissipating pattern.
When a vibrating membrane meets a barrier which is stiffer, denser or thicker, in which the speed of sound is greater, some of the energy of the vibration passes through the barrier and some of the energy is reflected. Thus, a soundboard when it meets the sound case in the usual harp construction reflects back some of the vibration energy into the board. However, the direction of that reflection varies in such a way that it dissipates the sound. In accordance with the second embodiment, an improvement in the sympathetic resonance system is achieved by reflecting the sound vibrations and concentrating them in a focused manner. More particularly, a structure is provided in the form of ridges along the edges of the soundboard, constructionally a "focus board" glued to the underside of the soundboard, which serves to reflect sound vibrations. This focus board defining the ridges around the soundboard is cut into a curve such that vibrations coming from one specific point will be reflected to, and concentrated at, a second point remote to the first point. In this manner, the sound waves are returned to the middle of the board where they can best activate the sympathetic resonance system.
In a further aspect of this embodiment, the focus board or ridges act in conjunction with a string strip. Harps are normally designed with a center string strip. This is secured centrally and axially to the soundboard, running from the bass end to the treble end. It is a narrow, rather thin board made of hardwood and typically consists of two pieces: one, which is thinner, is glued to the top of the soundboard; the other, which is thicker, is glued to the underside of the soundboard. The center strip and soundboard thereby define a three layer sandwich with the soundboard being the middle layer. Holes are drilled through this strip-soundboard-strip-sandwich throughout its entire length. The ends of the harp strings are threaded through the holes and secured by knots to the underside so that when they are stretched by the tuning pegs, they will pull against the board. Because of the thickness of the centerstrip sandwich, sound waves pass quickly up and down the soundboard and this helps greatly in the activation of the sympathetic resonance system.
In a preferred aspect of the second embodiment, the arrangement of the ridges defining the focus board is such that the points of focus are preferably at the points where the centerstrip ends. This is a point from which the sound waves can radiate out to the focus board barrier so that they can be reflected to be refocused onto the other end of the soundstrip. Examples of curves that can be used are ellipses and parabolas. In using a parabola for creating a focus board, the adjacent end of the centerstrip is disposed to lie at the focus point of the parabola. The ridges defining the focus board are advantageously formed of a material which is thicker and/or denser than the material of the soundboard, aiding in the reflection of the sound vibrations.
A further advantage of using the focus board is that it strengthens and reinforces the soundboard. The pull of the strings acting on the string strip in the center axis of the soundboard tends to pull the edges of the board inwardly, but which pull is resisted by the focus board. Thus, this embodiment synergistically combines with the first embodiment.
In a still further aspect of this embodiment, by placing the lowest bass string at the lowermost focal point of the focus board, an augmentation of the bass results. Wave forms from any string higher than this point are focused in the area between the end of the string strip and the lowest string. Therefore, the focus board catches the sound waves and returns them to the sympathetic resonance system, resulting in a harp having an excellent response to long sound waves, i.e., the bass tones.
A third embodiment of the invention is directed to eliminating the deleterious effect of the pillar or post securement on the bass tones of the harp. Traditional harp construction places the end of the pillar or post at the bottom of the soundboard where it contacts the end of the string strip. To keep everything in alignment, a large wood screw or bolt passes through the post, soundboard and soundcase. Variations in design have eliminated this wood screw or the use of a bolt at this point, but as a general matter, the resistance to the tension of the strings on the board remains concentrated in one small area at the end of the board and bottom of the soundcase. This area is referred to as the "yoke" and is one of the most troublesome parts of a harp. The tremendous accumulation of tension at this point exerts a shearing effect on the wooden parts of the harp and can cause harps to self destruct.
Besides creating a point of design weakness, the position of the post is very close to that of the lowest harp strings so that the clamped membrane effect on the soundboard is most pronounced on the bass tones. Indeed, on most large harps, the very lowest strings have such poor quality that they are rarely used. In effect, the action of the board on the lowest strings is so stiff that it can only give about a quarter of the response that a free vibrational mode would allow.
In accordance with the third embodiment, this weakness in the design of the yoke is eliminated, allowing more vibrational freedom to the board. In particular, the tension of the post is distributed across the entire lower surface of the soundboard and the sound case by means of a horizontal strut secured to and extending normal to the bottom end of the post on each side of the post and secured to the front side of the soundboard. The soundboard is formed with peg holes along its bottom end and the horizontal strut has pegs at corresponding locations sized to fit the holes, thereby securing the strut to the soundboard. The pegs are spaced from the post to allow as much freedom as possible to the soundboard. The result is a more resonant responsive board.
As a result of the foregoing three embodiments, a lightweight, inexpensive, sonorous, resonant, strong and easily-repaired harp is provided.